The present invention relates to an apparatus and a method for reading punched cards and, more particularly, to such apparatus, and method for reading gravity-fed punched cards.
Conventionally, a punched card comprises hole or perforation positions arranged in rows and columns. One widely used type of card shows 12 rows and 80 columns of hole positions.
Conventional punched card readers comprise a reading station and a drive mechanism for feeding the cards to the reading station. A common drive mechanism is made of a pair of punch rollers, at least one of which is positively driven. A card put into the reader is punched by the rollers and fed to the reading station at a controlled linear speed. A techometer coupled to the rotation of one of the rollers provides signals representative of the column positions while signals representative of the row positions are derived from the reading station itself.
While such a card reader is fully operative, the drive mechanism and associated card metering means add to its manufacturing and maintenance costs.
Another type of punched card reader has been devised to eliminate the above cost problems. Punch cards used with such a reader comprise clock marks representative of the column positions, for example. A row of such clock marks may be printed along an edge of the card, to be read by a mark sensor generating signals representative of the column positions while the card is driven through the reading station. An obvious drawback of this solution lies in that satisfactory operation of the reader depends on correct reflectivity and registration of the printed clock marks.